Hepatitis C (HCV) is a parenterally transmitted RNA virus that has been shown to be responsible for the majority of cases of NonA-NonB chronic active hepatitis. The virus causes considerable morbidity and mortality worldwide. Since discovery of the virus, considerable progress has been made in the development of qualitative and quantitative assays for patient diagnosis and management during antiviral therapy. Although current serum or plasma quantitative assays for HCV have proven utility, their correlation with the pathogenesis of HCV is poor and they offer limited diagnostic information for clinical management of patients during antiviral therapy. Our laboratory has recently developed a method for the direct detection of HCV RNA in peripheral whole blood which is more sensitive than current plasma or serum based HCV assays. Consequently, characterization and standardization of quantitative methods for assay of HCV in whole blood is worthwhile and may provide a more reliable means to correlate whole blood viral load with hepatic pathology and treatment of chronic infection. This proposal will address this hypothesis with three specific aims: 1) Building on our past observations, we will develop and standardize assays for the quantitation of HCV in peripheral whole blood. 2). Quantitative whole blood assays for HCV will then be used to investigate the relationship of whole blood viral levels with hepatic histologic activity indices. 3). Finally, we will measure the whole blood viral load of patients before, during, and following antiviral therapy. These experiments will test whether quantitation of HCV in whole blood can potentially improve our ability to predict patient outcome after therapy. The overall goal of this proposal is to establish the feasibility and clinical utility of quantitative methods for measurement of the virus in peripheral whole blood. We hope that this new technology will improve patient evaluation and management, as well as increase our understanding of the pathogenesis of HCV.